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The greenhouse effect. It's the mechanism warming the world as greenhouse gas levels rise. But it's not all bad. If Earth had no greenhouse effect at all, it would be too cold for us altogether. Just look at frigid, dry Mars.
溫室效應是指隨著溫室氣體濃度升高而使全球氣候變暖的機制。然而，這也不全是壞消息。如果地球上根本沒有溫室效應，那將會非常之冷。只要看看寒冷、干燥的火星就明白了。
Many thought that if Mars had a stronger greenhouse effect, it might be more hospitable to life. It's not a crazy idea. Mars has lots of carbon dioxide—much of it frozen. In the past, the CO2 as gas could have been in the atmosphere. And previous studies suggested that a denser CO2 atmosphere could have produced a warm and wet Martian climate.
許多人認為如果火星上也有較強的溫室效應，就可能更適宜生命生存。這個想法并不瘋狂。火星上有大量的二氧化碳——其中很多是以固態形式存在的。而在過去，二氧化碳可能是以氣體的形式存在于大氣中。之前的一項研究表明含高濃度二氧化碳的大氣會形成一個溫暖，潮濕的火星氣候。
But a new study throws cold water on that temperate Mars. Researchers ran global, 3D climate simulations for a variety of plausible Martian atmospheres. And even with a much thicker CO2 atmosphere, the greenhouse effect could not have warmed Mars above freezing. The study is in the journal Icarus.
然而一項新的研究卻向溫和的火星潑了冷水。研究人員用3D技術模擬了火星大氣合理的變化引起的氣候變化。即使大氣中的二氧化碳濃度更高，但溫室效應并不能將冰凍的火星暖化。這項研究發表在雜志《伊卡洛斯》上。
Mars has dry canyons and riverbeds, so water must have flowed at some point. But those flows may have been short-lived melting episodes triggered by volcanism or asteroid impacts. Because the idea of a balmy ancient Mars just got iced.
火星表面有干燥的大峽谷和河床，因此在某一時刻肯定有水流經過。但這些河流很可能因火山噴發或者小行星碰撞而消失，成為曇花一現。因此關于溫和的古代火星這個說法也被冰封了。
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